Calibration sleeves are known from the state-of-the-art whose inner diameter can be changed within a narrow range during operation. The inner diameter of the calibration sleeve is changeable for the purpose of manufacturing plastic pipes within required tolerances taking into account shrinkage of the plastic due to various factors. Examples of such calibration shells are found in DE 44 08 064 C1, DE-OS 26 16 197, DE 200 00 872 U1, DE 200 23 052 U1, EP 1 157 805 A1 and U.S. Pat. No. 2,981,975 to Steierman.
DE 198 43 340 C2 describes a calibration sleeve whose inner diameter can be adjusted during operation for plastic pipes with different outer diameters. This takes into account the fact that batches within orders are becoming increasingly small under today's production conditions, i.e., the extrusion systems have to be continuously adjusted. These adjustments lead to extrusion system downtime, require a great deal of labor to change the individual parts, and cause loss of plastic material. The calibration sleeve in DE 198 43 340 C2 has numerous rings of blades, and the individual blades of each ring are radially adjustable and overlap from radial plane to radial plane and closely adjoin each other at the overlapping areas. This creates an essentially tubular body that abuts the outside of an extruded plastic pipe, and its diameter is adjustable to adapt to the pipe diameter to be produced. The construction of this known calibration sleeve is relatively complex. In addition, a precisely circular cross-sectional plastic pipe cannot be fabricated with this calibration sleeve.
WO 2004/091891 A1 also describes a calibration sleeve that is adjustable during operation to the different external diameters of plastic pipes to be manufactured. This calibration sleeve possesses an inlet head to which two layers of flexible straps are attached. These straps cross each other like a lattice grate and are linked to each other at their crossing points. The calibration of the calibration sleeve needed for the inner diameter of the extruded plastic pipe is changed by pulling apart or compressing the lattice grate. This calibration sleeve is distinguished by a large adjustment range with high intrinsic strength. In addition, the numerous intersecting linked straps form an absolutely circular calibration sleeve with each adjusted diameter.